2.2. Data Sources

Data was accessed through the Institute for Clinical and Evaluative Sciences (ICES) through the Data Access Services division. The Ontario Drug Benefit (ODB) database was used to identify all patients engaged in OAT and to determine their past medication use of methadone or buprenorphine. The ODB database contains detailed records of all prescriptions dispensed to Ontario residents eligible for public drug coverage. In Ontario, residents are eligible for public drug coverage if they are aged 65 or older, reside in a long-term care facility, are disabled, are receiving social benefits for income support, or have high prescription drug costs relative to their net household income. Health system utilization was identified using the Canadian Institute for Health Information (CIHI) and the National Ambulatory Care Reporting System, and hospital admissions were identified using the CIHI Discharge Abstract Database. All diagnosis information from physician visits was determined using billing data from the physician Ontario Health Insurance Plan (OHIP) database. OHIP covers physician services for all permanent residents of Ontario. We obtained patient location of residence and demographic information from the Ontario Registered Persons Database, which contains a unique entry for each resident who has ever received insured health services. Patient information was linked anonymously across databases using encrypted 10-digit health card numbers. The linking protocol has been described extensively elsewhere [12, 13] and is used routinely for health system research in Ontario [14–16].